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Sunday, 17 May 2009

Sic Transit

Photo: Thierry Legault

Every now and then a photographer manages to capture a truly spectacular sight, and the image becomes instantly famous—so far, I've seen this one on the news, in newspapers, and in numerous places on the internet. Astronomical photographer Thierry Legault (he's authored several books on the subject, the most recent of which, The Art of Astrophotography, will be published in English translation in late 2009) took this "transit" photograph from a location in Florida, using a Canon 5D Mark II mounted to a Takahashi TOA-130 refractor telescope (effective focal length 2,200mm). Shooting through a Baader solar filter, the camera was set on ISO 100 with a 1/8000th shutter speed. Remarkably, the Shuttle Atlantis is traveling at 15,500 miles per hour, and the transit itself lasted only eight-tenths of a second, which gives you an idea of the depth of knowledge and preparedness required of the photographer. This transit was viewable from a swath of territory on Earth only three and a half miles wide.

The picture above, however, is a radical crop. Some great photographs are not designs that are composed merely for pictorial effect, but in this case you really must take a look at the full photograph at Thierry's website (fourth one down)—it's as stark and emblematic as any work of modern art, aesthetically perfect in addition to being a photographic report of something real and seldom seen.

Comments

He photographed two transits - the one you show is the first, with the shuttle at an altitude of 260km, and lasted only 0.3 seconds! I was amazed by his comment about the image: "The thin silhouette confirms that the cargo bay doors were opened." The image has enough resolution to distinguish a 2 meter wide feature at 260km - incredible.

this has been all over the net, but i still cannot see it enough. it's always good to have a reminder of how small even our largest creations are when compared to what exists in nature. gives you a sense of perspective :)

@John Camp: The effect is called "limb darkening". The wikipedia page describing it seems to be reasonably accurate from a quick skim. Essentially when you look at the solar limb, you are seeing less deep into the atmosphere than you are at the center of the disc, so it's cooler and therefore redder and dimmer.

Some of Thierry's photography is spectacular, and this transit is certainly no exception.

This site contains scores of high resolution images captured by the Hubble orbiting space telescope, some of them greater than a gigabyte in size when saved to your computer. (You have to click through to the "full resolution image" links.) Needless to say, you'll need a broadband connection. One mind-blowing image of the Carina nebula opens at a native resolution of nearly 48x100" at 300 ppi. As you repeatedly click on the "+" icon you just keep seeing more detail in the dust clouds and stars. And the thing is, you could drop our entire solar system into this image, and it would cover about three pixels.
Some of the images of spiral galaxies (M51 is my favorite) are breathtakingly beautiful. I printed this one at 17x24" and have it hanging on my wall; I keep finding myself standing in front of it, staring in slack-jawed astonishment.
Consider yourself warned.

JC,
Although not quite the same thing as limb darkening, you can see the effect in spheres frontally-lit by reflecting light, too, because there's less light reflecting back off the surface at the "edges" of what you can see. Here's a random example I pulled off the web....

I think this is a testament to Canon auto-focus technology that it locked on to the correct subject, Atlantis, despite being a small part of the whole frame, and the second object being so much farther away.

Re: Aizan's "next up: the clouds of venus? titan? the gas giants?", I went so far as to compare the angular diameter of the shuttle in the featured photo (pixel counting relative to the size of the sun in the photo, it's about 25" of arc), because it looked as if it might be comparable in size to some of the planets. It turns out that Saturn subtends 25-30" of arc, Jupiter 30-49", Venus 10-66", depending on relative positions in their orbits (this from "Angular Diameters" on Wikipedia). I didn't post because it gets a little ridiculous. Transit times are about 5 milliseconds and the shadow path on earth is about as wide as the shuttle itself, so it's a real challenge. Starting to take photos 2 seconds before the event and hoping for nice framing isn't going to work! Getting enough light in a short enough exposure to freeze the motion of the shuttle becomes the issue, instead of controlling the backlight. Nooooo!

One of the nice things about the latest batch of DSLR cameras is their wonderful high ISO performance.
There are a lot of moderately priced scopes out there with equatorial mounts that you could use as a guide.
Learn how to polar align the scope, put a 300 f4 (2.8 would be even better) on the camera and piggyback a 30 second exposure of M42 at about ISO 3200 and you will be amazed.
Heck on a dark night just lock the camera down with a fast prime for a star trails shot. I tried it with a D70 with an old 105 2.5 wide open and got nice color off Orion.
What fun. You don't have to spend the price of a nice car to give astrophotography a try.

This'll run you about $3,300 (the price of a fancy DLSR plus a lens or two). It's everything you need to do pretty serious astrophotography. Definitely NOT the least expensive way to go, but it's a sweet scope and camera. The mount is marginal; you'll need to take care to shield the scope from breezes and vibration. But it's usable

(BTW, I could trim a grand from the price tag by custom picking exactly what would suit my needs.)

As with terrestrial photography, great astrophotography depends more on skill than gear.